1. Field of the Invention
The present invention relates to a rear projection screen for use in a projection-type television or the like, and, more particularly, to a lens sheet such as a lenticular lens sheet that diffuses light entering the lens sheet from the rear side and allows the diffused light to emerge from the lens sheet toward the viewing side, and to a rear projection screen including such a lens sheet.
2. Description of Related Art
Rear projection screens, for which lenticular lens sheets whose base materials are made from synthetic resin materials such as PMMA (polymethyl methacrylate) are used either singly or in combination with other lenses (e.g., Fresnel lenses), have conventionally been known as rear projection screens for use in projection-type televisions or the like.
In general, a lenticular lens sheet for use in such a rear projection screen has lenses formed on the light-incident-side (rear-side) surface and extraneous light absorbers in the shape of stripes formed on those portions of the light-emergent-side (viewing-side) surface through which light (imaging light) converged by the lenses does not pass, so that lowering of image contrast that is caused by extraneous light entering the lenticular lens sheet from the viewing side can be prevented.
The extraneous light absorbers are usually formed with the use of black ink including a black-colored binder resin in which light-diffusing particles are incorporated. Since the black-colored binder resin contains light-diffusing particles, extraneous light that enters the lenticular lens sheet from the viewing side undergoes diffuse reflection. As a result, reflection of extraneous light that occurs on the surfaces of the extraneous light absorbers depending on the position of an extraneous light source or the like is effectively prevented.
However, the above-described conventional lenticular lens sheet has the following problem: since colorless, transparent particles such as silica are used as the light-diffusing particles to be incorporated in the extraneous light absorbers, the black-colored binder resin becomes thin in those spots where the light-diffusing particles are present, and this brings about decrease in extraneous light absorption. For this reason, the image displayed on the screen totally appears whitish brown (color faded) due to the extraneous light diffuse-reflected from the light-diffusing particles. In particular, when a rear projection screen including such a lenticular lens sheet is used in the open air, since extraneous light is strong, light is reflected in a larger amount, and the above-described problem thus becomes conspicuous.
It is possible to solve the above-described problem by incorporating no light-diffusing particles in the black-colored binder resin of the extraneous light absorbers. However, if light-diffusing particles are not incorporated in the black-colored binder resin, reflection of extraneous light heavily occurs on the surfaces of the extraneous light absorbers depending on the position of an extraneous light source or the like, as described above. Moreover, it is not easy to impart thixotropic properties to the binder resin without adding light-diffusing particles, and the binder resin containing no light-diffusing particles is poor in printability. It is therefore extremely difficult to form the extraneous light absorbers by printing with the use of the binder resin containing no light-diffusing particles. In addition, since the extraneous light absorbers made from the binder resin containing no light-diffusing particles have smooth, glossy surfaces, it is easy to recognize the unevenness of coating, and, moreover, the surfaces of these extraneous light absorbers are easily stained with fingerprints or the like.
On the other hand, in a projection-type television now in use, a transparent plastic panel is increasingly placed on the light-emergent side (viewing side) of a lenticular lens sheet as a protective plate for protecting the lenticular lens sheet contained in a rear projection screen.
However, if this lenticular lens sheet has extraneous light absorbers containing light-diffusing particles like the above-described conventional one, the plastic panel is scratched by the light-diffusing particles (by those parts of the light-diffusing particles protruding through the surfaces of the extraneous light absorbers) that come in contact with the plastic panel due to vibration caused while a projection-type television or the like including the lenticular lens sheet is transported.